[PATCH 3.2 14/77] mac80211: mesh: fix call_rcu() usage

Ben Hutchings
2015-12-24T15:44:08Z

From: Johannes Berg <johannes.berg@intel.com>

commit c2e703a55245bfff3db53b1f7cbe59f1ee8a4339 upstream.

When using call_rcu(), the called function may be delayed quite
significantly, and without a matching rcu_barrier() there's no
way to be sure it has finished.
Therefore, global state that could be gone/freed/reused should
never be touched in the callback.

Fix this in mesh by moving the atomic_dec() into the caller;
that's not really a problem since we already unlinked the path
and it will be destroyed anyway.

This fixes a crash Jouni observed when running certain tests in
a certain order, in which the mesh interface was torn down, the
memory reused for a function pointer (work struct) and running
that then crashed since the pointer had been decremented by 1,
resulting in an invalid instruction byte stream.

Fixes: eb2b9311fd00 ("mac80211: mesh path table implementation")
Reported-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/mac80211/mesh_pathtbl.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/mac80211/mesh_pathtbl.c
+++ b/net/mac80211/mesh_pathtbl.c
@@ -779,10 +779,8 @@ void mesh_plink_broken(struct sta_info *
static void mesh_path_node_reclaim(struct rcu_head *rp)
{
struct mpath_node *node = container_of(rp, struct mpath_node, rcu);
- struct ieee80211_sub_if_data *sdata = node->mpath->sdata;

del_timer_sync(&node->mpath->timer);
- atomic_dec(&sdata->u.mesh.mpaths);
kfree(node->mpath);
kfree(node);
}
@@ -790,8 +788,9 @@ static void mesh_path_node_reclaim(struc
/* needs to be called with the corresponding hashwlock taken */
static void __mesh_path_del(struct mesh_table *tbl, struct mpath_node *node)
{
- struct mesh_path *mpath;
- mpath = node->mpath;
+ struct mesh_path *mpath = node->mpath;
+ struct ieee80211_sub_if_data *sdata = node->mpath->sdata;
+
spin_lock(&mpath->state_lock);
mpath->flags |= MESH_PATH_RESOLVING;
if (mpath->is_gate)
@@ -799,6 +798,7 @@ static void __mesh_path_del(struct mesh_
hlist_del_rcu(&node->list);
call_rcu(&node->rcu, mesh_path_node_reclaim);
spin_unlock(&mpath->state_lock);
+ atomic_dec(&sdata->u.mesh.mpaths);
atomic_dec(&tbl->entries);
}